Level 1 — Absolute Beginner
A spacecraft called BepiColombo is flying to the planet Mercury. It left Earth eight years ago, in 2018.
BepiColombo was built by two space agencies. One is from Europe, called ESA. The other is from Japan, called JAXA.
Recently, the spacecraft dropped a part it does not need anymore. Now it is getting ready for the last, hardest part of its trip.
On November 21, the spacecraft will fire its engine one time to go into orbit around Mercury. If something goes wrong, controllers on Earth cannot fix it right away, because Mercury is very far away.
- spacecraft
- a vehicle used to travel and work in space
- planet
- a large round object in space that orbits a star
- agency
- an organization that does official work, like exploring space
- orbit
- the curved path an object takes around a planet or star
- engine
- a machine that makes something move
- controller
- a person who watches and directs a spacecraft's flight
- maneuver
- a planned and controlled movement
- journey
- an act of traveling from one place to another
Level 2 — Elementary
BepiColombo, a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), has entered the final stage of its long journey to Mercury. The mission launched in October 2018 and has spent eight years traveling toward the solar system's smallest and innermost planet.
Earlier this month, the spacecraft separated its Mercury Transfer Module, the part that carried fuel and solar panels for the long cruise, from its two science orbiters. Those orbiters, called the Mercury Planetary Orbiter and Mio, will now travel on together toward the planet.
The most critical moment of the mission comes on November 21, when the spacecraft must perform a single engine burn to slow down and be captured into orbit around Mercury. Because a radio signal takes several minutes to travel between Mercury and Earth, mission controllers cannot correct the burn in real time if something goes wrong.
The orbit insertion was originally planned for December 2025, but was delayed after engineers discovered a problem with the spacecraft's thrusters before an earlier flyby of Mercury. If November's burn succeeds, the two orbiters will separate from each other in December, and full scientific observations of Mercury are expected to begin in April 2027.
- innermost
- closest to the center, or in this case, closest to the sun
- transfer module
- a section of a spacecraft used to carry fuel and power equipment during travel
- orbiter
- a spacecraft designed to circle a planet or moon rather than land on it
- critical
- extremely important, often because failure would have serious results
- capture
- in spaceflight, the process of being caught by a planet's gravity into orbit
- radio signal
- a wireless transmission used to send information, such as commands to a spacecraft
- thruster
- a small engine used to control the movement or direction of a spacecraft
- flyby
- a spaceflight past a planet or moon without landing or entering orbit
Level 3 — Intermediate
The BepiColombo mission, a joint undertaking of the European Space Agency and the Japan Aerospace Exploration Agency, has entered the culminating phase of an eight-year interplanetary cruise following its October 2018 launch, as its two science orbiters shed the transfer module that had ferried them across the inner solar system.
With the Mercury Transfer Module jettisoned, the Mercury Planetary Orbiter and its Japanese counterpart, Mio, now proceed in tandem toward a rendezvous with the solar system's innermost and smallest planet. The spacecraft's trajectory has already included multiple gravity-assist flybys of Earth, Venus, and Mercury itself, each used to shed velocity gradually rather than relying on a single decisive burn.
That approach culminates on November 21, when the spacecraft must execute an autonomous orbit-insertion burn, a maneuver mission planners describe as carrying no possibility of real-time correction from ground controllers, given the several-minute communication delay between Mercury and Earth. A failure at this stage would jeopardize the entire scientific return of the mission.
The insertion date itself reflects an earlier setback: engineers detected an anomaly in the spacecraft's thruster system in 2024, ahead of a planned Mercury flyby, forcing planners to push the orbit-insertion date back by nearly a year, from the original December 2025 target. Assuming the burn succeeds, the two orbiters will part ways in December to pursue their separate scientific orbits, with coordinated observations of Mercury's surface, exosphere, and magnetosphere scheduled to commence in April 2027.
- culminating
- forming the climax or final stage of a process
- interplanetary
- occurring or existing between planets
- jettison
- to discard or release something no longer needed, especially from a vehicle
- rendezvous
- a meeting at an agreed time and place, especially between spacecraft
- gravity-assist flyby
- a maneuver using a planet's gravity to change a spacecraft's speed or direction
- autonomous
- performed independently, without outside control or intervention
- anomaly
- something that deviates from what is normal or expected
- exosphere
- the outermost, extremely thin layer of a planet's atmosphere
Level 4 — Advanced
The BepiColombo mission, a collaborative endeavor of the European Space Agency and the Japan Aerospace Exploration Agency, has entered the terminal phase of an eight-year interplanetary transit following its October 2018 launch, marked by the recent jettisoning of the Mercury Transfer Module that had sustained the spacecraft's science orbiters across the inner solar system.
Freed of its transfer stage, the tandem of the Mercury Planetary Orbiter and its Japanese counterpart, Mio, now proceeds toward a rendezvous with the solar system's innermost and least massive planet, having already shed substantial velocity through a sequence of gravity-assist flybys of Earth, Venus, and Mercury itself, an approach favored precisely because it distributes risk across many smaller maneuvers rather than concentrating it in one.
That risk nonetheless converges decisively on November 21, when the spacecraft must execute an autonomous, singularly consequential orbit-insertion burn, a maneuver mission planners characterize as admitting no prospect of real-time ground intervention given the multi-minute light-time delay separating Mercury from Earth. A failure at this juncture would imperil the entirety of the mission's anticipated scientific yield.
The insertion date itself bears the imprint of an earlier technical setback: an anomaly identified within the spacecraft's thruster architecture in 2024, discovered ahead of a scheduled Mercury flyby, compelled planners to defer the insertion by nearly a year from its original December 2025 target. Contingent on the burn's success, the two orbiters will subsequently part ways in December to assume their designated scientific orbits, inaugurating coordinated investigations of Mercury's surface composition, tenuous exosphere, and magnetosphere beginning in April 2027.
- terminal phase
- the final stage of a process, especially one leading to a critical event
- transit
- the act of passing through or across a space, especially over a long distance
- tandem
- two things arranged or acting in coordination with one another
- converge
- to come together toward a single point
- juncture
- a particular point in time, especially a critical one
- imperil
- to put something at serious risk of harm or failure
- tenuous
- very thin, slight, or weak
- inaugurate
- to begin or introduce a system, policy, or period
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